The --first-parent history can be ruined pretty easily by an inexperienced Git user. They'll use their local master as their feature branch for days and then they'll try to push it. Git will unhelpfully tell them to first do a "git pull" before pushing. So they do, which leaves them with a bullshit "merged master into master" merge commit and then they push that shit, thereby guaranteeing that --first-history will always omit the actual history of where origin/master was and instead take a trip through this dude's little feature adventure.